And you thought the East Germans spied a lot. A new study shows that the West Germans had fully 10,000 agents snooping on their Communist neighbors. And they knew about the Berlin Wall before it went up.

It’s a well-known fact that East Germany had agents crawling all over West Germany during the Cold War. Up to 6,000 of them, some in high places, were regularly passing information eastwards across the wall.

According to a new study published on Friday, though, when it came to recruiting spooks, the West Germans were even better. Fully 10,000 citizens of Germany’s communist half were spying for Bonn. Not only that, but West Germany’s intelligence agency the Bundesnachrichtendienst (BND) had a pretty good idea about the plans to build the Berlin Wall, but their bosses in Bonn simply didn’t want to believe them.

German historians Armin Wagner and Matthias Uhl have pored over files released by Germany foreign intelligence agency (BND) covering the period between the formation of the communist German Democratic Republic (GDR) in 1949 and the fall of the Berlin Wall in 1989. In their book “BND Against the Soviet Army,” they reveal that the agency managed to recruit thousands of people from all sections of East German society for military espionage.

Just before the Berlin Wall was built on Aug. 13, 1961, this network of spies informed the West Germans that something big was being planned “The BND knew something was up that July and August,” Wagner told SPIEGEL ONLINE. The agency likewise knew that a wall was a realistic scenario and told the politicians in Bonn. “But they didn’t want to accept the idea.” The BND couldn’t pinpoint exactly when West Berlin would be sealed off. “Until a week before the wall went up only around 60 people knew it was going to happen,” Wagner said.

Military espionage in East Germany was vital to the West at the height of the Cold War. According to Wagner, the 400,000 Soviet troops based in East Germany were the strongest Red Army divisions in the entire Eastern Bloc. The West feared an attack could be launched from the GDR on West Germany and NATO. “They needed reconnaissance,” he says.

That was where the spies came in. The West German agency recruited thousands of ordinary East Germans to keep them informed of any military build up. The spies used radio transmitters or passed information via visiting relatives from West Germany. The BND would then pass on the intelligence to the government and military.

These East German spies’ motivation varied enormously. For many the decision to spy was provoked by a deep-seated attitude of anti-communism. But others did so out of adventurism, or due to family ties, or simply as a favor to old army buddies from the war. There was also some financial compensation, though the study’s authors believe this was less important as a motivation, particularly as it was impossible to spend West German money in the East. “Bank accounts were sometimes opened in their names so that if they ever left the GDR they would have some start-up capital,” Wagner says.

East Germany Was Better at the Spying Game

Before 1961 it was relatively easy to recruit spies and to access the information they gathered. According to Uhl, the BND had already recruited 5,000 East Germans by 1955, most of them from the ranks of the defeated German army. Although things got more difficult after the wall went up, a network had already been established and new spies were recruited, for example, by conservative professors at the universities or journalists. The BND also increased its reliance on information passed on by West German tourists to the GDR.

The same game, of course, was being played in the other direction as well. Wagner points out that, “there were many in West Germany, particularly the 1968 generation, who were attracted by communist ideology and were ready to help the GDR.”

And despite the fact that West Germany had 4,000 more spooks that East Germany did, the GDR spies were significantly more successful at the espionage game. West German intelligence, for example, never managed to place agents high up in the East German government whereas Bonn was riddled with agents. The most famous was Günter Guillaume, who became a top aide to Chancellor Willy Brandt. He was uncovered in 1974, which led to Brandt’s resignation.

But what struck the study’s authors as most surprising was how much all the snooping became a part of everyday life. These were not professional agents, but ordinary people, “housewives and students.”

“West and East Germany have to be considered together” Wagner concludes. “Despite the division between the two states, the spying on both sides shows how closely connected the people really were.”